Control for air-operated motor



MaI'Ch 1958 I c. F. VOYTECH 2,825,353

CONTROL FOR AIR-OPERATED MOTOR Filed Dec. 9, 1953 25 .[ZZWZZZZOZ United States (ZONTROL FOR AIR-OPERATED Moron Charles F.- Voytech, Chicago, 111., assignor to Crane Packing Company, Chicago, 111., a corporation of Elinois Application December 9, 1953, Serial No. 397,193 4 Ciaims. (Cl. 137-36) This invention relates to a control for an air-operated motor and will be described with particular reference to a motor of the vane type which is adapted to turn a shaft at a relatively high speed.

Air operated motors are presently used to tighten or loosen screws, nuts and bolts, to operate drills and in many special applications. One such special application is in driving a rotatable tool known as a tube expander which is used to expand the ends of condenser tubes into their respective headers by an internal rolling operation to form a fluid tight connection therebetween. This conii'ection takes the place of packing formerly used for the same purposes. It has been found, however, that when an expander rolls a tube for a longer period of time than is necessary to effect a tight union between the tube and its header, the material of the tube operated upon by the expander will become brittle and the tube will then crack and leak in service.

To prevent an over-rolling of the tube in the aforesaid special application, it is desirable to stop the rolling at the point where a tight union will be efiected, all subsequent rolling being useless for this purpose and being responsible for the brittleness of the tube; The rolling can be stopped by the operator if he is skilled and can sense the correct point at which to stop the rolling operation. Such skilled operators, however, are difficult to obtain and it has been found that even with a skilled operator the rolling operation is not uniform from one tube to another.

It has been proposed to adopt automatic means for stopping the rolling operation when it is substantially complete. Such means utilize a motor which is slightly under-powered so that as the tool completes the rolling operation and then attempts to roll beyond that point, the additional resistance to rolling produced by the overrolling will cause the motor to slow down, and the slowing down of the motor is then utilized to operate a suitable control to stop the motor completely. Where the motor is an electric motor, the stopping can be accom- 'p'lishe'd by utilizing the increase in the current used to take care of the overload to operate a switch which opens a circuit to the motor and stops it automatically.

The electric control has been adapted to an air-operated motor, a small electric generator driven off the spindle of the air motor being used to generate a current the value of which varies with the speed of the air motor. in this case, a decrease in the current developed below a predetermined value is utilized to operate the stopping mechanism. This type of control is somewhat more complex than is desirable and furthermore involves the use of electrical equipment at the shaft of the motor which may cause sparks and constitute a fire hazard.

One of the characteristics of an air operated motor is that the volume of air leaving the exhaust of the motor is directly proportional to the speed of the motor, assuming that the line pressure to the motor is constant. Thus, if the exhaust volume decreases with a constant line pressure, it may be assumed that the motor is overloaded and has accordingly slowed down. Thus, the volume of air exhausted may be taken as an indication of the torque load on the air motor.

This invention has forone of its principal objects the provision of a control for an air operated motor which will stop the motor upon a predetermined overload condition, the means utilizing a variation in exhaust pressure occasioned by an overload to operate the stopping mechanism for the motor.

A more specific: object of this invention is to provide a control for an air operated motor wherein the air intake of the motor is controlled by an electromagnetic device and wherein the exhaust air" from the motor is utilized to operate a switch which is adjusted to open a circuit when a predetermined overload condition exists in the motor as indicated by the decrease in the volume of airfiowing in the exhaust from the motor. The making or breaking of a contact is then used to operate the electromagnetic cont'rol for the motor to shutoff the air supply and thereby stop the motor.

A still more specific object of this invention is to provide, for an air operated motor, a control mechanism for the motor which utilizes what is known as 'a wind switch operated by the exhaust air from the motor to control an electromagneticallyoperated valve in the intake pressure line to the motor.

These and other objects of this invention will become apparent from the following detailed description when taken together with the accompanying drawings in which Fig. l is a schematic diagram of an air motor incorporating the automatic overload control of this invention;

Fig.- 2 is a cross section through the motor showing the vanes which are typical of such motors; and

Fig. 3 is a schematic diagram of a modification of a portion of the control for the'airmotor.

Referring now to the drawings for a detailed'deseription of the invention, thetool to be driven is shown at 10, and for purposes of illustration is comprised of a body member 11 mounted on a shaft 12 and having mounted thereon in tapered relation with respect to the axis of shaft 12, a plurality of rollers 13; The taper is very slight and is intended to expand a tube 14 into an opening 15 provided in a tube sheet 16 of a condenser or the like. It is contemplated that tool 10 will be rotated and adto form a fluid tight seal betwen itself and tube sheet 16.

'It is contemplated further that the rotation of tool 10 will be stopped when the fluid tight seal is achieved so that there will be no over-rolling of the tube such as will result in crystallization of the material of the tube which subsequently would cause the tube to crack in service and cause a leak.

Tool 10 is mounted in a suitable chuck 17 which is rotatable with the shaft of an air motor 18 of readily available standard manufacture. The driving means for the motor is shown schematically in Fig. 2 and is comprised of a plurality of vanes 19 disposed for radial reciprocation in slots 20 in the rotor 21 of motor 18. Said rotor 21 is mounted eccentrically with respect to the housing 22 of the motor so as to contact the housing at'23 with a sealing cont-act and to provide a space 24 increasing in volumefrom point 23 to the point diametrically opposite thereto. An inlet port 25 disposed to the left of point 23 as viewed in Fig. 2 is connected to the intake or inlet conduit 26 through which air under pressure is admitted to port 25. An outlet port 27 is formed in housing 22.and is connected to outlet or exhaust conduit 28 Motor 18 is provided with a suitable handle 29 by which it may be held and controlled as will be pointed out hereinafter.

I Air under pressure is supplied from a suitable source (not shown) to a valve 30, the body of which may be subkeeps contacts 54 andSSseparated, i a

stantiallybylindriegl and provided with a round bore 31.

A cylindrical valve of the balanced type is disposed 'in bore 31' and is comprised of spaced lands 32 and 33 form- I ing between them a peripheral groove 34. The stem 35 of the valve extends outwardly from the valve body and into V thefcenter of a: solenoid 36 to constitute thearmature thereon An inlet port 37 is connected by an extension of conduit 26 t0 the aforementioned source ofjair under a pressure and an 'outlet port 38 is connected to conduit 26 to conduct the air under pressure from valve to' th e air motor. a l

L "The control circuit forsolenoid 36 includes :a lead 39 connected to one; terminal 40 of a suitable'source of electrical,energy (not shown), and a lead 41- havingrtwo branches 42 and 43. Branch 42 contains theautomatic overload control of this invention shown at 44, and bran'c'h'43 contains-a manual reset switch ,45 located .on handle29 and'connected inrshunt with'the contro'l:44. A a

upon vanes 67' drops toawalue corresponding'to the motor speed at which the' maximum j torque loadris pressure exerted by the jet issuing from nozzle 70 upon vane 57 decreases and s'pringi61 is allowed to rotate vane 57 and lever 58 in a counterclockwise direction until finger 68 strikes prong 67andlopens contacts 69 It is contemplated that the tension of spring .61 will be such that contacts '69 will open when the pressure of the jet attained and at which the rhetoric to he stopped. Inasmuch astspring 6,1 of. the c0ntrol44Iwillhold contacts 69' in their open position when motor 18 is stopped,

manuaLstart switch 46, likewiselocated in:the handle;29,

tis co'nnected in'series with control 44 and itsshuht. switch a "45; and with a lead 47 connected to theother terminal 48 .of the aforementioned suitable source of electrical energy.

- Valvei30 is designed to be ope'ned when solenoid 376 .is'

V energized and closed by' springpressure When solenoid 36 i i is' deenergized, 'so"that if there is a power failure, the motor 18 will be automatically disabled'and stopped. To, this end valve 3!} isprovidedawith a helical'spring 49 compressed between land 32 and, a washer 50 'held'by a snap ring 51"in the upper end of the valve as'viewed' in Fig. 1. Spring 49 holds the valve in a position to'cutofi communication between ports'37 and 38. A stop in the form of'a snap ring 52 is provided adjacent land 33 to hold it thegvalvei in'closed position and to limit the movement "of the valve. Whensolenoid 3.6 istenergized, the'valve is shifted againstthe'action of-springi49 to a'zposition to allow'port 37 to acomrnunicatewith port 38 through Vgroove34. 7 I i';

. a Manually controlled switch '46 in handle 2915 designed to be normally ope'n'and to be closed when it is desired to start motorl18; Thus switch 46 is'comprised of a pivoted lever 53 havingta contacti54 adapted to cooperate with a fixed contact: 55 in handle 29. A spring 56 normally The automatic control by which valve 30.is closed when thetorque load on tool 10 reaches a predetermined value is comprised of a cup-shaped vane;57 mounted on a lever r 58 pivotedsatn59 to a fixed part of the c ontrol; The

opposite end 60 0f lever'58 is connected by'a t'ension "spring 61'to.an adjustable abutment comprised'of a screw .62 threaded in a boss 63, and a lock-nut- 64. a The tension ,in'spring filtmay be adjusted to any'desired value to rege ulate the amount of air'pressure required to 'be ex'erted a'gainst cup 57 to cause lever'58 to rotate about its pivot :59; Mounted in control'44is a switch 65 havin'gia short i Iprong 66 and a long prong-67, the'latter being adapted to 1 be contacted by atfinger 68 formed in 'the end 60 of lever TV ji'g58 andat right angles "to the planeithereof A pair of V contacts69is mounted in opposed relation on prongs 66" a'nd67; respectively, the contacts being normally closed,

but opened when lever58 is rota'ted 'in a counterclockwise direction about its pivot 59' by'spring 61 this action causing the end of finger 681to strike the long prong 67 a nd Vur'geit awaysfrom prongj66to separate For opLencon-j tacts 69." a a a The outletcon'duit 28 passes.throughanopeninin con-J ftrol 44"and terminates in a nozzle: 70 which directs the; iexhaust air from 'motor'lfia'gainst the concave side of vane '57." ffhecontrol is 'suitably vented to prevent ,a buildup toffaif'fronrno'zzle 7 0; Thus, when-tl 1ejexhaust pressure is of pressure therein which wouldadversely afiect theflow T170 7 1; highiandjovercornesispring dhjvane 5 7 will'b'e rotated gclockwise aboutjpivot 5 9 and willaallow contacts '69 to 'closdfthereby completing ftheicircuit to solenoidt'36 and ding Ya s in t nenl os t n-v' whsi zmoto meadows,asee er so that less exhaustedgthe V fin Fig. 31s shown a modification of the control 44 uti- "'li zinga 'bellows arrangenient in place of the vane 57l "Thus conduit 28 is provided with a venturi 74Ywhich is i connected by means of, a pipe 75 toqthefinterioir" @116]: lows 76. Said bellows-76fis of the-metaltypeand isl in j'her'emiy' resilient so that it will fljno'rmally tend .toassnme; 7 a predetermined volume; {The endofbellowsf76:secured, 'Ito pipe 7-75 is stationary 'twhile the opposit "end 7 71 s l d that is, when no air pressure is exerted up'onvane 57ithe circuit through solenoid'36 will be open and hejoperation of valve 30 to its open position cannot be effected} To 7 enable motor 18 to start when control 44 is conditioned to open contacts 69, a shunt switch 45' is used, said switch r being connected on one side to lead 43 and on the other: 1' side to a lead 71 connecting contact 54 to said 'switch 45; 1 Thus, to startmotor 18;. switch'45 and manual startswitch'146 are operatedflto energize solenoid'36, and after motor 18 has attained itsi running speed-so th'atthe exhaust a 'jet is sufliciently strong to move vane '57 to'allow contacts 69 to closeQsWitch 45 is released'while contacts54and 55 7 remain ;closed; thereby; providing a ;complete;.cir cuit through the closed contacts 69 toisolenoid 36 ta a In the operation of thedevice, assuming that terminals a 4i) and 48 are connected't'o a suitable source of electrical energy suchtas the usuallllOt'volt 60'cycle line, theitool It) is applied to the work 'to be performed, lever 53-isi squeezed againsthandle 129 ,tocclo'se, contacts-54am '55 1i and thelthumb oflthe operator may be .used toi press switch 45 to completethelshunt circuit aroundfcontrol '44 torsolenoid 36. QThe energization ofsolen'oid'36 opens f valve 30 to admit air under pressure to conduit-'26 and f thence throughtthejinlet pqrt 25 to' theniotorflSI jA s the motor gains speed the exhaust air from the motor'will'bei" conducted through theconduit 28. through noz zzlef'lfifwith 7 increasing force andagainst vane 57 torotate said vane in a clockwise direction until prong 67jis released'and;

contacts 69 are closed. gkfter motor ls is running atiits operative speed, switch 45 is released but lever-53' is marnk tainedin'theen gaged position of contacts 54 and 555 As the tool 10 continues to operate it will eventually finish a I its'work and the torque load impressedupon the tooiby the work'will increase to' the pointwheremotor'18will a i beg'iri'to slow down. Theslowing downof-motor'lS-i L7 7 reflected-in a decreaseinthe amount of air exhausted I 'thtoughbonduit 28 which in turn decreases the pressure ofjthelrair'leaying nozzle 70 aud'hence vane-57 will be turned in a counterclockwise direction by spring 6 1,fthe,

1 spring pressure always ba n'cing thejressure otthe air" 1 issuing from nozzle 70. .Whenfthe pressure ofnthe' air.

"reachesa'predetermined value, finger" 68 will move prong '67 totheright as viewed in Fig. l tot open contacts 69,; t thereby rdeenergizing solenoid;36 and p ern'iitting sp'ring V V 49 to move the .valve 'to'it s closed position, In the closed r 7 positionof'the valve, motor-118, o f course' ceasesfto oper j ate;

at' i contacts a e. o n 'may e e u at dby' regulating the amount of airissuing from nozzle 70, This "maybe done by providing afbranch conduit 72 in exhaust a line 28 which 'is open toiatmosphere, andthen regulating the amount of the opening by means: ottaabutterfly valve 7 73. if desired, the 'positio'nsof the Vanna-maybe suit- 7 ably indicated and calibrate-if; a

to move axially relative to pipe 75. Said end 77 is also hermetically sealed with respect to said bellows 76 so that as pressure within said bellows varies and the bellows contracts or expands, end 77 will be moved axially relative to pipe 75. The axial movement of end 77 is imparted to a rod 78 which is adapted to contact prong 67.

In the operation of the modification showing Fig. 3, as motor 18 rotates at its operative speed the exhaust air in conduit 28 will pass through the venturi 74 and in so passing will create a suction or a reduced pressure in pipe 75 which in turn will reduce the pressure within bellows 76. This will cause end 77 and its associated rod 78 to move to the left away from prong 67, thereby enabling contact 69 to close and to energize solenoid 36. As the speed of motor 18 decreases, due to an overload imposed upon tool 10, and the volume of air passing through conduit 28 correspondingly decreases, the pressure in pipe 75 increases, thereby allowing bellows 76 to expand and move end 77 and its associated rod 78 to the right as viewed in Fig. 3. This movement eventually results in contact with prong 67 and in the opening of contacts 69 to deenergize solenoid 36 and close valve 30. The butterfly valve 73 may be used in connection with the modification showing Fig. 3 if desired.

It is understood that the tool may be a screwdriver, a wrench, a drill, or any other tool which is rotated as it operates and that the scope of the invention therefor is not to be limited to the form disclosed but is to be determined by the appended claims.

I claim:

1. In combination, a portable rotatable pneumatic motor including a driven shaft, the operation of which is to be stopped when the torque thereon exceeds a predetermined value, said motor being of such power as to reduce its speed when said predetermined torque value is reached, a supply conduit for conducting motive air to said air driven motor, an outlet duct conducting the exhaust air from the motor, said motor developing an exhaust flow which decreases as the speed of the motor decreases, a

valve disposed in said supply conduit, an electromagnet cuit for said electromagnet including a pair of contacts, and a movable vane disposed in said exhaust conduit and operatively connected to said contacts, said vane being responsive to the passage of air through said exhaust conduit and being operable when the rate of flow of air through said conduit attains a predetermined minimum to open said contacts and thus deenergize the electromagnet.

2. The combination described in claim 1, a bleed valve in the exhaust conduit ahead of the vane, said bleed valve being adjustable to vary the flow of the air striking the vane and hence to vary the torque at which the motor is stopped.

3. In combination, a portable rotatable pneumatic motor including a driven shaft, the operation of which is to be stopped when the torque thereon exceeds a predetermined value, said motor being of such power as to reduce its speed when said predetermined torque value is attained, a supply conduit for supplying motive air to said motor, an outlet duct for conducting the exhaust air from the motor, said motor developing an exhaust flow which decreases with the speed of the motor, a valve disposed in said supply conduit, an electromagnet controlling the operation of said valve and operable upon 'energization thereof to open the valve, an energizing circuit for the electromagnet including a pair of contacts, and means operatively connected to said contacts and operable when a predetermined minimum rate of flow of air through said exhaust conduit is attained to open said contacts.

4. The combination set forth in claim 3 wherein said contact operating means comprises an expansible bellows having one end thereof connected to said contact, a venturi disposed in said exhaust duct, and an air passage extending from the venturi and communicating with the interior of the bellows.

References Cited in the file of this patent UNITED STATES PATENTS 1,713,442 Mateovich May 14, 1929 1,864,127 Flanders June 21, 1932 2,239,738 Russell Apr. 29, 1941 2,670,001 McElvenny Feb. 23, 1954 

